This invention relates to aircraft navigation systems and methods.
In recent years, ground proximity warning systems (GPWS) have been developed and installed in all commercial aircraft. GPWS were designed to assist pilots in preventing controlled flight into terrain (CFIT), the cause of a large proportion of fatal aircraft accidents. Various problems exist with state of the art GPWS systems, including giving the warning too late for the pilot to recover, ignoring GPWS warnings because of disbelief on the part of pilots, and inability to climb over terrain in time to avoid CFIT when the terrain is rising too steeply.
Various attempts have been made to provide a temporary local map based on a terrestrial database combined with the aircraft""s longitude and latitude information, but such systems are too complex for the majority of pilots, and do not provide the most pertinent information, i.e., current, real time minimum safe altitude and projected minimum safe altitude. Furthermore, such systems provide the terrestrial information combined in a display with much other information, including, for example, weather information, which can be confusing to pilots who are accustomed to navigation based on minimum safe altitude data.
Currently there is no available source of minimum safe altitude data correlated to geographic information in electronic form. Use of lap books containing minimum safe altitude for a collection of cells, each cell representing a geographic area of the earth, is still the state of the art in aerial navigation. Such lap books must be updated periodically, and current U.S. regulations require updating every 56 days in order to provide pilots with the most current information. In view of the problems caused by the use of lap books, it has been proposed to add MSA data to enroute, terminal, and approach charts, which would require the pilot to constantly monitor the chart by cross checking the aircraft""s position while trying to complete flight duties. Additionally the pilot would have to interpret the relative position of the aircraft and determine if the aircraft would be entering a higher MSA.
In addition, in the United States but not in most other countries, air traffic computers have been designed to help air traffic controllers (ATC) monitor each aircraft""s altitude with regard to the minimum safe altitude (MSA) and to provide the ATC with an aural or visual warning, in which case the controller is supposed to give a verbal warning to the pilot to check the aircraft""s altitude. These systems are called minimum safe altitude warning systems (MINSAW). The MINSAW system depends on the ATC to immediately warn the pilot, and depends on the pilot being on a designated frequency; as a result, frequently the pilot is not warned in sufficient time to take appropriate corrective action.
Because of these problems with the state of the art, it is the objective of the present invention to provide a system and method for displaying the real time MSA of an aircraft based on its geographical position. A further object is to provide a system and method of displaying projected MSA.
These objects, and others which will become apparent in view of the following description, are achieved by the present invention which, in one aspect, comprises an navigation system comprising a global positioning receiver adapted to provide real time longitude, latitude, altitude, heading, velocity, and time data; a minimum safe altitude database for a collection of cells, each cell representing a geographic area of the earth; an alphanumeric display; and a processor adapted to calculate the minimum safe altitude for a cell corresponding to the real time latitude and longitude of the aircraft and one or more adjacent cells and controlling the display to indicate the real time numeric minimum safe altitude.
In another aspect, the invention comprises a method of aiding aerial navigation comprising: providing a database of minimum safe altitudes for a collection of cells, each cell representing a geographic area of the earth; providing an aircraft with a global positioning receiver; providing an alphanumeric display in the cockpit of the aircraft; using the real time longitude, latitude, altitude, heading, velocity, and time data from the global positioning receiver and the minimum safe altitude data from the database to calculate and display in numeric form on the alphanumeric display the real time minimum safe altitude.
Preferably the processor controls the display to indicate the projected MSA, which is generally accomplished by use of MSA information in cells in the database which are adjacent to the cell in which the aircraft is currently flying. The exact position, heading, velocity, and time data received from the global positioning system receiver is used to determine the location of the plane and the expected location.
The database preferably comprises airport approach data, including glidepath altitude, so that when the processor calculates that the aircraft is approaching an airport, it determines whether the approach is normal or not, and if normal, the MSA for the glidepath only is displayed. If the system determines that the landing approach is aborted, it displays the real time MSA and the MSA of the area beyond the airport, i.e., the projected position, when appropriate.
The MSA database is preferably updated periodically, for example every 56 days as required under current U.S. regulations.
An alarm is also preferably provided and the processor is adapted to cause the aural alarm to sound if the aircraft falls a certain distance, e.g., 200 feet, below the MSA, based on the global positioning data received from the global positioning system (GPS). An advantage of the present system is that the display in such case can also indicate the actual MSA for the cell into which the aircraft is travelling, so that the pilot can know exactly which altitude must be achieved in a climb.